1. Field of the Invention
The present invention relates to a write precompensation amount setting method and apparatus, which tune a write precompensation amount of a magnetic disk device, and more particularly, to a write precompensation amount setting method and apparatus for reducing a compensation shift which becomes problematic in a magnetic disk device.
2. Description of the Related Art
When magnetically recorded digital data is reproduced with a magnetic head, a peak shift occurs on a reproduced waveform. This peak shift is caused by a mutual interference with an adjacent bit (magnetized region) when a magnetized region corresponding to a bit array is read with a magnetic head. If the peak shift increases, a read pulse cannot be obtained at a position determined by a data window, which leads to a read error. The peak shift of this type is not too problematic when a recording density is low, but is problematic when the recording density is high. A method of compensating for a peak shift is a tuning method where the phase of a pre-identified bit, when data of a particular bit array whose peak shift is problematic, is recorded. In other words, a method compensating for a write operation (write precompensation).
Conventionally, a write precompensation amount according to an environmental temperature is determined at an ordinary temperature for each head as a drive parameter, and uniformly set for each environmental temperature in normal cases.
FIG. 1 is a flowchart showing the conventional process for setting a write precompensation amount.
Firstly, error rates are measured at ordinary and low temperatures in a test drive (step S1). For example, respective error rates are measured when a write precompensation amount at an ordinary temperature (such as 25 degrees centigrade) with a write current 40 mA, and a write precompensation amount at a low temperature (such as 5 degrees centigrade) with a write current 50 mA are changed between 15 and 30% in steps of 1%.
Next, the write precompensation amounts at the best (minimum) error rates among the error rates measured in step S1 are determined as optimum write precompensation amounts at the ordinary and the low temperatures in the test drive (step S2). For example, if the write precompensation amounts at the lowest error rates at the ordinary temperature of 25 degrees centigrade and the low temperature of 5 degrees centigrade are respectively 20 and 24%, a deterioration amount from 25 to 5 degrees centigrade is determined to be 4%.
Then, an error rate at an ordinary temperature is measured at the time of mass production (step S3). By way of example, each error rate is measured when the write precompensation amount at the ordinary temperature of 25 degrees centigrade with the write current 40 mA is changed between 15 and 30% in steps of 1%.
Furthermore, the write precompensation amount at the lowest error rate among the error rates measured in step S3 is determined to be an optimum write precompensation amount at the ordinary temperature at the time of mass production (step S4). For example, the write precompensation amount at the lowest error rate at the ordinary temperature of 25 degrees centigrade is determined to be 20%.
Lastly, an optimum write precompensation amount at a low temperature is set according to the deterioration amount determined in steps S1 and S2 at the time of mass production (step S5). By way of example, the deterioration amount of 4% from 25 to 5 degrees centigrade, which is determined in step S2, is added to the write precompensation amount of 20% at the lowest error rate at the ordinary temperature of 25 degrees centigrade, so that the write precompensation amount at the low temperature is set as 24%.
However, the environmental temperature characteristic of each magnetic head may vary. Actually, a magnetic head whose write characteristic deteriorates significantly at a low temperature requires a large write precompensation amount. Therefore, a lack of compensation occurs. At the same time, for a magnetic head whose write characteristic is good at a low temperature, over-compensation occurs. Namely, any heads whose characteristics shift from an average head characteristic can possibly cause error rate deterioration. This loss cannot be ignored toward future improvements in the performance of a magnetic disk device, and more accurate tuning has been demanded.